Passive smoke may cause increased risk of stroke

The increased risk of stroke that comes with smoking may extend to non-smokers who live in the same household and breathe in second-hand smoke, a US study suggests.

Researchers found that non-smokers who had a stroke were nearly 50 percent more likely to be exposed to second-hand smoke at home than people who had never had a stroke.

During the study, stroke survivors exposed to second-hand smoke were also more likely to die from any cause compared to those without second-hand smoke exposure.

"Second-hand smoke is a risk to all people, but those with a history of stroke should take extra care to avoid it," said lead author Dr Michelle Lin of the Johns Hopkins School of Medicine in Baltimore.

One in four non-smokers (58 million people) in the US are still exposed to second-hand smoke, according to the Centers for Disease Control and Prevention.

"While cigarette smoking has long been known to increase the risk of stroke, less is known about the relationship between second-hand smoke and stroke," Ms Lin said by email.

To explore the question, the study team analysed data on nearly 28,000 people over 18 who had never smoked in the annual National Health and Nutrition Examination Surveys.

Participants were recruited between 1988 and 1994 and again between 1999 and 2012. They were asked, "Does anyone who lives here smoke cigarettes, cigars, or pipes anywhere inside this home?"

To gauge the amount of smoke people were exposed to, blood tests for cotinine, a breakdown product of nicotine, were performed on each participant.

The researchers also looked at other factors that might influence stroke risk or likelihood of second-hand smoke exposure like race, sex, education and income level.